From backpacks to 'flash-bangs': Boston's week of terror

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Photos:Boston bombings: The week in photos

The second of two explosions goes off near the finish line of the Boston Marathon on April 15, 2013. Three people were killed and at least 264 were injured in the double bombings.

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Photos:Boston bombings: The week in photos

A man comforts a victim at the scene of the first explosion.

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Photos:Boston bombings: The week in photos

Runners react near Kenmore Square after the explosions.

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Photos:Boston bombings: The week in photos

Rescue workers tend to the wounded on the scene. First responders tried to save lives and limbs before transporting victims to hospitals.

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Photos:Boston bombings: The week in photos

On April 16, 2013, a vigil was held at Boston's Garvey Park for 8-year-old bombing victim Martin Richard. The other victims were Krystle Campbell, a 29-year-old restaurant manager from Medford, Massachusetts, and Lingzi Lu, a 23-year-old Chinese national attending graduate school at Boston University.

On April 17, 2013, a federal law enforcement source with firsthand knowledge of the investigation told CNN that a lid to a pressure cooker -- thought to have been used in the bombings -- had been found on a roof of a building near the scene. It was one of several pieces of evidence authorities found.

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Photos:Boston bombings: The week in photos

The device also had fragments such as nails, BBs and ball bearings, the FBI said.

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Photos:Boston bombings: The week in photos

On April 18, 2013, the FBI released photos and video of two suspects in the bombings and asked for the public's help in identifying them.

FBI Suspect No. 2, later said to be Dzhokhar Tsarnaev, is apparently seen in this picture, far left in white cap. The photo was taken by Boston Marathon runner David Green at the scene of the bombings.

Late on the night of April 18, 2013, police responded to a call that a campus officer at the Massachusetts Institute of Technology was shot and killed. Police said a man later reported being carjacked by the brothers. The two were stopped in Watertown, Massachusetts, where police said they threw explosives and shot at the officers. One man, assumed to be Dzhokhar Tsarnaev, drove off. The other, later identified as Tamerlan Tsarnaev, was injured. He died at the hospital.

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Photos:Boston bombings: The week in photos

Boston Police Commissioner Edward Davis speaks to the media on April 19, 2013, and explains that the city is on lockdown until the surviving suspect is found.

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Photos:Boston bombings: The week in photos

Officers scoured Watertown, Massachusetts, where Dzhokhar Tsarnaev was last seen.

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Photos:Boston bombings: The week in photos

Frightened residents were questioned near Dzhokhar Tsarnaev's home in Cambridge, Massachusetts.

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Photos:Boston bombings: The week in photos

SWAT teams conducted door-to-door searches in Watertown while looking for the suspect.

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Photos:Boston bombings: The week in photos

Ruslan Tsarni, uncle of the Tsarnaev brothers, gave an interview April 19, 2013, outside his home in Montgomery Village, Maryland. He urged Tsarnaev to turn himself in.

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Photos:Boston bombings: The week in photos

SWAT teams continue to search in Watertown on April 19, 2013.

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Photos:Boston bombings: The week in photos

On the evening of April 19, 2013, a Watertown resident called the police and reported seeing a man on a boat in his backyard. Residents ran from the area where police said Dzhokhar Tsarnaev was hiding on Franklin Street.

Police threw "flash-bangs" -- devices meant to stun people with a loud noise -- and started negotiations with Tsarnaev. He eventually surrendered and was transported to a local hospital in serious condition.

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Photos:Boston bombings: The week in photos

People wave U.S. flags in Watertown after it was announced that Tsarnaev had been captured.

Two young men with backpacks walked with purpose down Boylston Street Monday afternoon, weaving through the crowd on the sidelines of the Boston Marathon. It seemed like they'd been there before, like they knew where they were going.

The one in the white cap reached his destination first, about two blocks from the finish line. The other one, wearing a hoodie and a black cap, kept going. Some three minutes later, he elbowed his way through the crowd and dropped his backpack near the finish line. It was about 15 minutes before 3 p.m.

The first explosion, at 2:50 p.m., sent smoke and flames into the air -- and glass and nails and ball bearings and BBs into the crowd. It seemed to inflict the cruelest kind of damage to any marathon fan: It attacked their legs.

Jeff Bauman, who survived but lost both legs, saw the man in the black cap drop his bag. Two women standing nearby -- restaurant manager Krystle Campbell and Chinese grad student Lingzi Lu -- died in the blast.

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As some people fell and others ran screaming, the man in the black cap casually walked away.

Twelve seconds later, another explosion, more screams, more panicked people running. This time, a little boy, Martin Richards, 8, lay on the sidewalk, fatally injured. His mother and sister also were seriously hurt. In the crowd, the man in the white cap strolled calmly and turned the corner onto Fairfield Street.

Later, an official who asked not to be named told CNN: "When the bombs blow up, when most people are running away and victims were lying on the ground, the two suspects walk away pretty casually.

"They acted differently than everyone else."

That night, a few minutes after 8, a college student using the screen name J_tsar tweeted a quote from rapper Jay-Z:

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Photos:Photos: Manhunt for Boston bombers

Photos:Photos: Manhunt for Boston bombers

Manhunt for Boston bombers – Boston bombing suspect Dzhokhar Tsarnaev is detained by officers on Friday, April 19. After a car chase and shootout with police, one suspect in the Boston Marathon bombing, Tamerlan Tsarnaev, was shot and killed by police early Friday, and his brother and second suspect, Dzhokhar Tsarnaev, was taken into custody Friday night. The two men are suspects in the bombings at the Boston Marathon on April 15, that killed three people and wounded at least 170. See all photography related to the Boston bombings.

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Photos:Photos: Manhunt for Boston bombers

Manhunt for Boston bombers – Special imaging techniques employed by Massachusetts State Police reveal Boston Marathon bombing suspect Dzhokhar Tsarnaev hiding in a boat in a backyard in Watertown on April 19.

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Photos:Photos: Manhunt for Boston bombers

Manhunt for Boston bombers – Dzhokhar Tsarnaev gets out of the boat he was hiding in outside of a home in Watertown, as seen in a surveillance video still.

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Manhunt for Boston bombers – An ambulance carries Boston Marathon bombing suspect Dzhokhar Tsarnaev, 19, from the scene after he was apprehended in Watertown, Massachusetts, on April 19.

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Manhunt for Boston bombers – Police SWAT teams leave the area after apprehending the suspect in a yard where he was hiding in a dry-docked boat on April 19.

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Photos:Photos: Manhunt for Boston bombers

Manhunt for Boston bombers – Residents flee from an area where a suspect was hiding on Franklin Street on April 19.

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Manhunt for Boston bombers – SWAT team members run toward a police assault on a house as gunfire erupts on April 19.

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Manhunt for Boston bombers – People react while watching police respond to reported gunfire on April 19.

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Manhunt for Boston bombers – SWAT team members move down residential streets as they perform door-to-door searches in Watertown, Massachusetts, on April 19.

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Manhunt for Boston bombers – A U.S. military helicopter lands behind Watertown Mall as law enforcement agencies continue to search for the 19-year-old bombing suspect on Friday.

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Manhunt for Boston bombers – SWAT teams prepare to enter a home as they continue the door-to-door search.

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Photos:Photos: Manhunt for Boston bombers

Manhunt for Boston bombers – U.S. President Barack Obama meets with members of his national security team in the Situation Room of the White House on April 19 to discuss developments in the Boston bombings investigation.

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Photos:Photos: Manhunt for Boston bombers

Manhunt for Boston bombers – SWAT team members line a residential street in Watertown, Massachusetts, as the manhunt continues on Friday.

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Photos:Photos: Manhunt for Boston bombers

Manhunt for Boston bombers – A man watches from the window of a home as a SWAT team member keeps watch on Friday, in Watertown, Massachusetts.

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Photos:Photos: Manhunt for Boston bombers

Manhunt for Boston bombers – Police to continue to the door-to-door search on Francis Street in Watertown, Massachusetts, on Friday.

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Photos:Photos: Manhunt for Boston bombers

Manhunt for Boston bombers – Law enforcement officers place themselves in an overhead position on Arsenal Street as the search continues on April 19.

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Photos:Photos: Manhunt for Boston bombers

Manhunt for Boston bombers – Law enforcement officers react to what was initially thought to be a threatening suspect on Arsenal Street on April 19.

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Photos:Photos: Manhunt for Boston bombers

Manhunt for Boston bombers – A police SWAT team searches houses on April 19 for the second suspect.

Manhunt for Boston bombers – A Massachusetts state trooper watches other troopers line up at Watertown Mall as the manhunt for the second suspect continues in Watertown on Friday.

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Photos:Photos: Manhunt for Boston bombers

Manhunt for Boston bombers – Police continue the ongoing manhunt for the second suspect on Williow Avenue in Watertown on Friday.

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Manhunt for Boston bombers – A Watertown police vehicle with bullet holes in its body and a shattered windshield is towed out of the search area on April 19 in Watertown, Massachusetts.

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Manhunt for Boston bombers – A Massachusetts State Police officer checks the bag of a cyclist amid heightened security on Friday in Watertown.

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Photos:Photos: Manhunt for Boston bombers

Manhunt for Boston bombers – Katia Costa looks out her window as police continue the manhunt on Nichols Avenue in Watertown on Friday.

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Photos:Photos: Manhunt for Boston bombers

Manhunt for Boston bombers – Ruslan Tsarni, uncle of the Boston terror suspects, told CNN affiliate WBZ that Tamerlan "got what he deserved" in an interview outside his home in Montgomery Village, Maryland, on Friday.

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Photos:Photos: Manhunt for Boston bombers

Manhunt for Boston bombers – A woman is questioned by Cambridge police and other law enforcement agencies Friday near the home of the second suspect in Cambridge, Massachusetts. A Massachusetts Institute of Technology campus police officer was shot and killed late Thursday night at the school's campus in Cambridge. A short time later, police reported exchanging gunfire with alleged carjackers in nearby Watertown.

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Photos:Photos: Manhunt for Boston bombers

Manhunt for Boston bombers – SWAT teams move into position at the intersection of Nichols and Melendy avenues in Watertown, Massachusetts, on Friday.

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Manhunt for Boston bombers – SWAT teams gather at the intersection of Nichols and Melendy avenues in Watertown while searching for the remaining suspect on Friday.

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Manhunt for Boston bombers – Onlookers take pictures while SWAT team members look around on Friday.

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Manhunt for Boston bombers – Massachusetts Gov. Deval Patrick, left, speaks to the media at a shopping mall on the perimeter of a locked-down area during the search on Friday.

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Photos:Photos: Manhunt for Boston bombers

Manhunt for Boston bombers – Metro SWAT members hang off the back of a truck during the search on Friday.

Suspects tied to Boston bombings – Dias Kadyrbayev, left, with Boston Marathon bombing suspect Dzhokhar Tsamaev in a picture taken from the social media site VK.com. Kadyrbayev is expected to plead guilty August 21 to charges in connection with removing a backpack and computer from Tsamaev's dorm room after the April 2013 bombing, according to a defense lawyer.

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Photos:Photos: Suspects tied to Boston bombings

Suspects tied to Boston bombings – Bombing suspect Tamerlan Tsarnaev was killed during the shootout with police in Watertown, Massachusetts, on April 19, 2013. He is pictured here at the 2010 New England Golden Gloves.

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Photos:Photos: Suspects tied to Boston bombings

Suspects tied to Boston bombings – Dzhokhar Tsarnaev was captured in a Boston suburb on April 19, 2013, after a manhunt that shut down the city. In July, he pleaded not guilty to killing four people and wounding more than 200.

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Photos:Photos: Suspects tied to Boston bombings

Suspects tied to Boston bombings – From left, Azamat Tazhayakov and Dias Kadyrbayev went with Boston bombing suspect Dzhokhar Tsarnaev to Times Square in this photo taken from the social media site VK.com. A federal grand jury charged Tazhayakov and Kadyrbayev with obstructing justice and conspiracy to obstruct justice relating to the removal of a backpack from Tsarnaev's dorm room after the bombings. Tazhayakov was convicted of conspiracy and obstruction charges in July 2014. He faces up to 25 years in prison at his sentencing in October. He has filed an appeal.

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Photos:Photos: Suspects tied to Boston bombings

Suspects tied to Boston bombings – Robel Phillipos, a U.S. citizen, was also arrested on May 1, 2013. He was charged with lying to federal agents about the bombing, according to court papers.

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Photos:Photos: Suspects tied to Boston bombings

Suspects tied to Boston bombings – Phillipos, Tazhayakov and Kadyrbayev are accused of removing items from Tsarnaev's dorm room after the bombings on April 15, 2013. The items they took included a backpack containing fireworks that had been "opened and emptied of powder," according to the affidavit.

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Photos:Photos: Suspects tied to Boston bombings

Suspects tied to Boston bombings – The FBI released photos and video on April 18, 2013, of two men identified as Suspect 1 and Suspect 2 in the deadly bombings at the Boston Marathon. They were later identified as Dzhokhar Tsarnaev, 19, and his brother Tamerlan Tsarnaev, 26.

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Photos:Photos: Suspects tied to Boston bombings

Suspects tied to Boston bombings – Boston Police released surveillance images of Dzhokhar Tsarnaev at a convenience store on April 19, 2013.

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Suspects tied to Boston bombings – The FBI tweeted this photo on April 19, 2013, and urged Watertown residents to stay indoors as they searched for the second suspect.

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Photos:Photos: Suspects tied to Boston bombings

Suspects tied to Boston bombings – The FBI released photos and video on April 18, 2013, of two men it called suspects in the deadly bombings and pleaded for public help in identifying them. The men were photographed walking together near the finish line.

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Photos:Photos: Suspects tied to Boston bombings

Suspects tied to Boston bombings – A man identified as Suspect 2 appeared in this photograph by bystander David Green, who took the photo after completing the Boston Marathon. Green submitted the photo to the FBI, he told Piers Morgan in an interview.

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Photos:Photos: Suspects tied to Boston bombings

Suspects tied to Boston bombings – The man identified as Suspect 2 appears in a tighter crop of David Green's photo.

Tamerlan Tsarnaev, one of the Boston Marathon bombing suspects, was the subject of an April 2009 photo essay that appeared in a graduate school magazine at Boston University. According to the article, he had hoped to become a naturalized American and make the U.S. Olympic boxing team. Authorities say an overnight shootout with police left him dead on April 19, 2013.

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Photos:Boston bombings suspect: Tamerlan Tsarnaev

Tsarnaev answers a call while walking to boxing practice at the Wai Kru Mixed Martial Arts center in Boston.

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Photos:Boston bombings suspect: Tamerlan Tsarnaev

Tsarnaev practices boxing at the Wai Kru Mixed Martial Arts center.

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Photos:Boston bombings suspect: Tamerlan Tsarnaev

Tsarnaev shows how he strengthens his ankles, according to the photo essay. The photographer did not want to be named for this story.

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Photos:Boston bombings suspect: Tamerlan Tsarnaev

Though he had lived in the United States for five years, Tsarnaev said in the essay: "I don't have a single American friend. I don't understand them."

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Photos:Boston bombings suspect: Tamerlan Tsarnaev

Tsarnaev works out.

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Photos:Boston bombings suspect: Tamerlan Tsarnaev

Tsarnaev stretches during boxing practice.

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Photos:Boston bombings suspect: Tamerlan Tsarnaev

Tsarnaev tapes up his hand.

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Photos:Boston bomber Dzhokhar Tsarnaev

Photos:Boston bomber Dzhokhar Tsarnaev

Dzhokhar Tsarnaev was arrested on April 19, 2013, after a massive manhunt. An overnight shootout with police killed the other suspect -- Tsarnaev's 26-year-old brother, Tamerlan. A jury condemned Tsarnaev to death on Friday, May 15, for his role in killing four people and wounding hundreds more.

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Photos:Boston bomber Dzhokhar Tsarnaev

On April 18, 2013, the FBI released photos and videos of two suspects and asked the public to help identify them.

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Photos:Boston bomber Dzhokhar Tsarnaev

Dzhokhar Tsarnaev was found on April 19, 2013, in a boat that was dry-docked in the backyard of a Watertown home. He was covered in blood from bullet wounds.

Tsarnaev stands in court, flanked by his lawyers, in this sketch from July 2013.

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Photos:Boston bomber Dzhokhar Tsarnaev

An image posted to the social sharing website Reddit purportedly shows Dzhokhar Tsarnaev being detained by law enforcement officers.

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Photos:Boston bomber Dzhokhar Tsarnaev

Tsarnaev was seen on this convenience store surveillance video that was released by the Boston Police Department.

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Photos:Boston bomber Dzhokhar Tsarnaev

A still of the suspects from footage released by the FBI after the bombing.

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Photos:Boston bomber Dzhokhar Tsarnaev

Additional photos and video were released by the FBI.

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Photos:Boston bomber Dzhokhar Tsarnaev

A picture of Tsarnaev from his apparent profile on VKontakte, a Russian social network similar to Facebook.

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Photos:Boston bomber Dzhokhar Tsarnaev

The Boston Police Department also released this undated photograph of Tsarnaev.

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But J_tsar was a chatterbox on Twitter. Early Tuesday, just past midnight, he sent out another, more mysterious tweet: "There are people that know the truth but stay silent & there are people that speak the truth but we don't hear them cuz they're the minority."

All day Tuesday, the news focused on the gruesome details of the crime scene and those who were lost or maimed. More than 170 people were hurt by flying glass, shrapnel, ball bearings and nails, some of them grievously. The sidewalks along Boylston Street were slick with blood in some spots.

President Obama condemned the marathon bombings as terrorism and vowed that those responsible would feel the full weight of justice.

Sometime that day, a college student named Dzhokhar Tsarnaev came into Gilberto Junior's body shop in the suburb of Somerville. Junior said he had known Dzhokhar for about two years and that he had a taste for expensive cars and clothes. Dzhokhar had dropped the car off two weeks earlier, said it was his girlfriend's and then "disappeared."

He quoted the rapper Eminem: "Nowadays everybody wanna talk like they got somethin to say but nothin comes out when they move their lips; just a bunch of gibberish."

He slapped down an Internet rumor that a man had planned to propose to his girlfriend at the marathon but found her dead: "fake story."

He replied to someone else's tweet: "and they what 'god hates dead people?' Or victims of tragedies? Lol those people are cooked."

And he tweeted: "So then I says to him, I says, relax bro my beard is not loaded."

Behind the scenes, federal investigators began to sort through what has become the norm in a post-9/11 society: Thousands upon thousands of surveillance photos and videos taken from cameras at traffic lights, store fronts, parking garages and other places along the marathon route.

The crime scene extended for 12 blocks. The 26.2-mile marathon route is open to the public and the event is heavily photographed. Authorities asked for amateur cell phone photos and videos from anyone who had been at the marathon. Who might investigators find on the sidelines, in the background?

During a shift change at the Boston Police Department, a supervisor told officers: "When you get home tonight hug your kids once and then hug them again. And that's an order."

As Tuesday melted into Wednesday, J_tsar was back on Twitter. "I'm a stress free kind of guy," he tweeted shortly before 2 a.m.

The day seemed like any other at school for the Mercedes-driving 19-year-old later identified as the tweeter: Dzhokhar Tsarnaev, a sophomore at the University of Massachusetts-Dartmouth. His student ID told the story of his day; like all students, he has to swipe the card to enter buildings on campus.

Card swipe information shows he went to the gym and spent Wednesday night at his dorm. Dzhokhar was known as Jahar to friends on campus.

Student Zach Bettencourt said he discussed the bombing with Dzhokhar at the gym.

"You hear about this kind of thing happening in Iraq and Afghanistan but not here," Bettencourt said.

Less than 48 hours after the bombing, Harry Danso was making small talk with Dzhokhar at their dorm. "He was just in the hallway, said 'Hi' and walked past me. He just acted regular. Gave me a regular smile, like usual."

"He was just relaxed," the student said, asking the paper not to publish her name. Also on Wednesday, authorities revealed that one and possibly both of Monday's deadly devices had been fashioned out of pressure cookers. A pressure cooker lid was found on a rooftop near the marathon finish line.

Meanwhile, Dzhokhar's older brother, Tamerlan, was reaching out to family members. He called two uncles on Thursday, seeking their forgiveness.

"He called me, confused," Ruslan Tsarni, who lives outside Washington, told CNN. In an earlier interview with USA Today, another uncle quoted Tamerlan as saying, " 'I love you and forgive me' ... I guess he knew what he had done."

They already had made progress, finding clear images of the men with the backpacks and ball caps on a surveillance video. Intelligence had been developed on one suspect earlier in the week; images of the second suspect were isolated Wednesday, officials told CNN.

Jeff Bauman, who'd survived the bombing but lost both legs, regained consciousness at Boston Medical Center and gave them a lead. On a piece of paper, he wrote: "Bag, saw the guy, looked right at me."

Top level officials from the Justice Department, FBI, ATF, Department of Homeland Security, Massachusetts State Police and Boston Police Department debated whether they should go public with the images they had found.

By 5 p.m. Thursday, after several delayed news briefings, a task force of federal, state and city law enforcement officials released photographs of the man in the black cap and hoodie and the man in the white cap. They asked for the public's help in identifying them.

"We are processing all the digital photographic evidence we can," Agent Richard DesLauriers, who leads the FBI's Boston division, told reporters. He asked the public to keep submitting their photos to police, noting that investigators had "a huge amount of video evidence to process."

Later that evening, an image of one of the brothers was captured on surveillance video at a convenience store in Cambridge. Then, about 11 p.m., police learned that Sean Collier, a police officer at the Massachusetts Institute of Technology, had been ambushed and shot to death in his patrol car on the campus.

In the early hours of Friday, the pair allegedly carjacked a Mercedez-Benz SUV in Boston, forced the driver to withdraw cash at an ATM, then let him go at a gas station.

The driver called 911 and reported that he'd been held up at gunpoint by two men who said they were the marathon bombers. He also said he'd left his cell phone in the car.

Police were able to track the cell phone -- and the car -- to Watertown, just west of Boston.

Just before 1 a.m. Friday, a lone Watertown cop came upon the brothers, who were now driving two cars, police Chief Edward Deveau said. They were armed with guns, pipe bombs and other explosives. Both cars stopped and the brothers leaped out and opened fire before backup could arrive.

Other officers responded to the pinned-down officer's call for help. More than 200 shots were fired in 5 to 10 minutes.

Deveau said the brothers tossed explosives at police, including a homemade pressure-cooker bomb.

The older brother, Tamerlan, walked straight toward the cops but ran out of ammunition. He'd been wounded. An officer tackled him and police were handcuffing him when Dzhokhar tried to escape in the Mercedes. He aimed the car at the officers, who dove out of the way, and he ran over his brother. The Mercedes dragged the older brother down the street as it sped away.

The driver continued to exchange gunfire with police, then jumped out of the SUV and ran into the darkness.

Authorities finally got names to go with the photos and videos when they scanned a fingerprint from the brother left behind, according to The New York Times. He was Tamerlan Tsarnaev, and he was pronounced dead at a hospital. He was wearing explosives and a triggering device.

Police also learned that the Russian government had asked the FBI to check out Tamerlan's connections to radical Islamic groups in 2011. Nothing had come of the investigation.

Boston woke up Friday morning and learned the names of both bombing suspects. The manhunt for Dzhokhar Tsarnaev lasted all day and shut down much of Boston as police asked everyone to stay indoors. Authorities searched door-to-door in Watertown.

By then, there were a couple thousand police officers at the scene. A thermal image photograph, released Saturday by state police, showed what authorities say was Dzhokhar Tsarnaev lying in the middle of the boat.

"We know you're in there. Come out with your hands up," police demanded over a bullhorn.

Officers spotted Dzhokhar poking through the tarp and used "flash-bangs," devices meant to stun people with a loud noise. They used a robot to pull the tarp off the boat and negotiated with Dzhokhar for about half an hour.

Police, who had no idea whether he had explosives with him, repeatedly told him to stand up and lift his shirt and he eventually complied.

"Once we saw that, we felt comfortable enough to send some officer tactical equipment to grab him and pull him away from the boat," Deveau said.

The Boston Police Department got the last word on Twitter: "CAPTURED!!! The hunt is over. The search is done. The terror is over. And justice has won. Suspect in custody."

A few minutes later, a more somber tweet followed as Boston heaved a sigh of relief:

"In our time of rejoicing, let us not forget the families of Martin Richard, Lingzi Ly, Krystle Campbell and Officer Sean Collier."